Alkyl styrenes, including styrene, are important starting materials for organic chemical industry, mainly used for producing polystyrenes, ABS resins, SBR rubbers, and unsaturated resins. Up to now, styrene based resins rank worldwide only after PEs and PVCs in terms of production.
The conventional process for producing styrene involves dehydrogenating ethyl benzene, which is a greatly endothermic reaction and requires a great input of heat energy, leading to a reaction temperature of more than 600 degrees centigrade. In view of this, the prior art has developed a process wherein (alkyl) styrenes are directly synthesized by alkylating alkyl benzenes (e.g. toluene) on the side chain in the presence of an alkaline catalyst with an alkylating agent (e.g. methanol), which has been identified as a promising production process due to low cost, low consumption of energy, little environmental pollution, simple procedure and easy availability of the starting materials, and drawn more and more attention. Chinese application No. CN200910201632.3 discloses a process for producing ethyl benzene and styrene by alkylating toluene by methanol on the side chain, wherein the catalyst to be used, by weight, includes 60-99% of a mesoporous carbon carrier, and supported thereon, 0.1-30% of an oxide of alkali metal or alkali earth metal and 0.1-10% of a boron oxide. Chinese application No. CN201010261714.X discloses a process for producing ethyl benzene and styrene by alkylating toluene with methanol on the side chain, wherein the catalyst is ion-exchanged by a K salt before use.
In the alkylating process, toluene and methanol react mainly through the following two routes in the presence of an alkaline catalyst.

In the presence of the alkaline catalyst, toluene reacts mainly in line with the routes (1) and (2), and at the same, a very minor amount of co-product like xylene or methyl ethyl benzene is produced. However, under this reaction condition, methanol per se will decompose into CO and H2, as illustrated by the following route (3):

From the standpoint of economical value, it is required that as much as possible methanol be converted into ethyl benzene and styrene by reacting with toluene, rather than unnecessarily consumed by this decomposition. When other alkyl benzenes or alkylating agents (e.g. dimethoxy methane) are to be used for the alkylating process, there is a similar concern.
Therefore, there still exists in the prior art a need for an alkylating process for alkyl benzenes, which is capable of effectively inhibiting decomposition of the alkylating agent (especially methanol), whereby improving the utilization efficiency of the alkylating agent.